None
Not Applicable.
The present invention relates in general to the transmission of torque and more particularly to a torque coupling and to an automotive vehicle equipped with the coupling for apportioning torque between wheels of the vehicle.
Most light automotive vehicles, such as automobiles, sport-utility vehicles, vans and light trucks, have four wheels, but in the typical vehicle the engine which propels the vehicle is coupled to only two of the wheels. In older vehicles the rear wheels were normally used for propulsion, but in newer vehicles it is commonly the front wheels. To be sure, some early vehicles had four-wheel drivexe2x80x94the Army Jeep for examplexe2x80x94but that type of vehicle often operated with power delivered to only two wheels. If the need arose for more traction, the engine was coupled with the other two wheels through a manually operated transfer case. The rear and front wheels share the torque delivered by the engine under a fixed ratio.
In recent years automotive manufacturers have produced some of their more sophisticated vehicles with so-called xe2x80x9call wheel drivexe2x80x9d. In the typical vehicle of this type all four wheels normally drive the vehicle with the engine torque split between the front and rear wheels. The engine delivers its power through a transmission which is in turn connected directly to two of the wheelsxe2x80x94the primary driving wheels. The remaining two wheelsxe2x80x94the secondary driving wheelsxe2x80x94are connected to the transmission through a torque coupling which accommodates slight variations in speed between the primary and secondary wheels. To be sure, a differential is interposed between primary driving wheels and the transmission, but the connection is direct in the sense that no slippage can develop between the primary wheels and the transmission. Another differential exists between the coupling and the secondary wheels, but the coupling allows for slippage between the secondary wheels and the transmission, so the connection in that sense is indirect. The torque coupling divides the torque between the primary and secondary wheels.
Morever, some all wheel drive vehicles have couplings that have the capacity to vary the torque between the primary and secondary wheels to better accommodate varying road and operating conditions. With this type of vehicle, all of the torque delivered to the secondary wheels passes through a clutch in the torque coupling, and as a consequence the coupling is large and heavy. Apart from that, it is complex, often containing a multitude of plates and a complicated mechanism for urging the plates together with variable force. Actually, the torque transferred through such a clutch depends not only on the force exerted on the plates, but also the slippage between the plates and temperature as well. This renders control of the clutch difficult.
A torque coupling includes a clutch and a planetary set connected such that two torque-transfer paths exist through the couplingxe2x80x94one a mechanical path and the other a clutch path. A clutch in the clutch path accommodates slippage in the coupling and controls the amount of torque transferred in each of the paths. The proportion of torque transmitted through the mechanical path in comparison to the torque transmitted through the clutch path is determined by the design of the planetary set and its ratios. The invention also resides in an automotive vehicle having primary and secondary wheels and a power unit, with the power unit being connected directly to the primary wheels and also being connected to the secondary wheels through the torque coupling. The amount of torque transmitted through the clutch of the torque coupling controls the apportionment of torque between the primary and secondary wheels.